1. Field of The Invention
This invention relates to unique proto-oncogene sequences derived using recombinant DNA technology and to the production and use of these sequences as well as the expression products thereof.
2. Related Art
Advances in recombinant DNA technology have led to the discovery of normal cellular genes (proto-oncogenes) which control growth, development, and differentiation. Under certain circumstances, regulation of these genes is altered and they become oncogenes which cause normal cells to assume neoplastic growth behavior. There are approximately 40 known proto-oncogenes to date, which fall into various categories depending on their functional characteristics. These-include, (1) growth factors and growth factor receptors, (2) messengers of intracellular signal transduction pathways, for example, between the cytoplasm and the nucleus, and (3) regulatory proteins influencing gene expression and DNA replication.
Several oncogenes and proto-oncogenes are known to encode more than one product by using alternatively spliced mRNAs. These include the SV40 T antigen gene, c-src, c-Ha-ras, c-abl and c-myb. Alternative splicing includes or excludes particular coding sequences within the mRNA, which is eventually translated. Consequently, the biological function of a single gene can be expanded by the splicing choice. Previous reports have shown that an alternatively spliced c-myb mRNA encodes a truncated form of the c-myb p75 which includes the DNA binding region and nuclear localization signal present in c-myb protein, but lacks regulatory regions required for transcriptional activation (Weber, et al., Science, 249:1291, 1990). The truncated protein has been shown to interfere with the function of c-myb during differentiation of mouse erythroid leukemia cells.
Many proteins cooperate with each other in the activation of transcription from specific promoters. Through this cooperation, the gene can be transcribed and a protein product generated. Members of the Fos proto-oncogene family, along with members of the Jun gene family, form stable complexes which bind to DNA at a specific site designated AP-1. The AP-1 site is located in the promoter region of a large number of genes. Binding of the Fos/Jun complex activates transcription of a gene associated with an AP-1 site. In cells that have lost their growth regulatory mechanisms, it can be envisioned that this Fos/Jun complex may "sit" on the AP-1 site, causing over expression of a particular gene. Since many cell proliferative disorders result from the over expression of an otherwise normal gene, such as a proto-oncogene, it would be desirable to identify methods which interfere with the excessive activation of these genes.
For many years, various drugs have been tested for their ability to alter the expression of genes or the translation of their messages into protein products. One problem with existing drug therapy is that it tends to act indiscriminately and affect healthy cells as well as neoplastic cells. This is a major problem with many forms of chemotherapy where there are severe side effects primarily due to the action of the toxic drugs on healthy cells.
In view of the foregoing, there remains a need for therapeutic agents which specifically inhibit the over expression of genes associated with cell-proliferative disorders, but have limited negative effects on healthy cells.